Process of making water-resistant molded lignocellulose



Patented Oct. 19, 1954 UNITED STATES PROCESS OF MAKING WATER-RESISTANT MOLDED LIGNOCELLULOSE Donald F. Othmer, Coudersport, Pa, and Edmund Mellenger, Douglaston, and Warren R. Smith, Crown Point, N. Y.

No Drawing. Application May 11, 1951, Serial No. 225,926

This invention relates to a method of preparing bonded mixtures of lignocellulose and sulfur by pressing said mixtures under the application of heat, and it also relates to the bonded and pressed products produced by said method in the form of wallboard and similar materials.

Herein the term lignocellulose is used to describe either the liberated fibers as obtained after any grinding or defibrating means, and also the naturally occurring unliberated fibers as they exist in Wood in any form, including sawdust, slabs, edgings; or in bagasse and other annual plant residues, and the like.

Fibers or particles of wood and annual plant material have been formed and compressed into wallboard by wet processes or methods for many years. The wet process used varies from company to company and compares closely with paper making. The raw materials (such as fiber, waterproofing agents and sizes) and the methods of production are similar. Chips from cordwood (not waste Wood such as sawdust, shavings, slabs) are made into fibers of a particular mesh size by one of several methods, usually involving expensive equipment and processing steps. The fibers are washed, refined, screened, and fed to a Fourdrinier machine similar to the standard paper making machine, where the board is formed as a thick continuous mat, known as wet lap. After this wet lap is trimmed and cut to size, the individual pieces are placed on screens and inserted between the steam heated platens of a press and pressed at pressures of 1000 pounds per square inch or higher for 30 minutes or longer. A large amount of water is removed in a heating cycle long enough to dry and cure or bond the materials into a firm mass. To reduce the long pressing cycle, the mat may be pre-pressed first to remove much of the water, or sent through a very large drier. Equipment such as chippers, high pressure boilers, and washers, besides all the special handling and loading machines used in such prior art processes, are very expensive. This high cost of breaking whole wood or wood logs down into its individual fibers and the attendant complications and skill required in the subsequent operations indicates that the making of wallboard by the wet process must be a very large business enterprise by itself and not something to be appended to an existing wood working industry.

In addition to the wet process of making wallboard, substantially as described above, there have been introduced Within the past ten years or so, three different types of processes utilizing resins. These are:

(1) dry powdered synthetic resin is mixed with substantially dry wood fiber, the moisture content of wood varying from 1-15%; and a dry forming and pressing process is used;

(2) synthetic resin in a liquid solution or dispersion is added to relatively dry wood fiber, the

2 Claims. (Cl. 106-163) moisture content of which is less than 5%; and a dry forming and pressing process is used;

(3) synthetic resin in a liquid solution or dispersion is added to a wet slurry of wood fiber; and a wet forming process is used.

The synthetic resins used in the above processes are not only expensive, ranging up to 25 to 40 cents per pound, and therefore having a value much more than any wood waste used, but the percentage of the resins based on the wood waste used is high since it may be from 10 to 25%, although lower amounts have been used with poor results. In some cases the producer of such resin bonded boards has actually found himself in the chemical business of making the required resins or purchasing them on a large scale, rather than keeping to his own business of wood working or wood processing.

It is an object of our invention to produce a bonded product of the nature of wallboard by compressing and heating lignocellulosic material of whatever origin or variety with sulfur.

It is also an object of our invention to produce a bonded product of the nature of wallboard by compressing and heating lignocellulosic fibers of whatever origin or variety with sulfur and lignin.

Another object of our invention is to provide a method of producing in a dry process, inexpensive, water resistant and permanently bonded products of varying thicknesses, densities, hardnesses, shapes, and having other similar desirable properties.

These and other objectives are readily apparent upon reading this disclosure of our invention:

According to our invention we prepare a mixture of lignocellulose material; for example, sawdust or wood fiour, and sulfur; and we thereafter subject the prepared mixture to specific temperature and pressure ranges for definite periods of time to effect a permanent bond between the lignocellulose and the sulfur.

The species of wood used may beof the deciduous type or of the coniferous type; or it may be a lignocellulose material from any of the annual agricultural products such as bagasse, cocoanut fibers, and the like.

The preferred size of the lignocellulose is from 16 to 30 mesh, though mesh sizes above'and below this range are operable, particularly long fibers or thin shavings up to one inch square or larger have been used. It is desirable that the least dimension of the particle be not over about 1 5'.

The sulfur we use is of a commercial, technical grade quality and is referred to as flowers of sulfur. It is also possible to use other allotropic forms of elemental sulfur, for example, monoclinic, rhombic and the like, in this process.

Ground or comminuted wood prepared by any mechanical process as, for example, from an attrition mill, hammer mill, stone mill, or from any combination of a steam and mechanical dis- 3 integrating process, such as the Asplund or Masonite process, and the like, can be used.

The moisture content of the lignocellulose to be used may vary considerably, and it is preferred that the lignocellulose possess not more than the naturally occurring amount of mois ture. Lignocellulose containing substantially to about 50 percent moisture (based on its total weight) may be used. Thus, for example, fresh sawdust, or bagasse, either having a moisture content up to about 50 percent, or sawdust having the normal air-dry moisture content of about percent, as well as bone-dry sawdust, are all operable and give satisfactory results in our process.

It is often advantageous to add additional lignin to increase the strength of the cured board. The lignin we use consists substantially of the non-polysaccharide constituents of wood and other lignin containing plants and is that part of the plant which does not dissolve in a specified concentration of sulfuric acid under specified physical conditions. Lignin containing more or less cellulose is commercially available as a lay-product of various paper making processes using wood or other lignocellulose from either trees or annual plants, such as (1) the soda process, and (2) the sulfate or kraft process, and (3) the sulfite process. Lignin may also be obtained from lignocellulose by using various acid hydrolysis processes. Substantially any lignin from processes separating it more or less completely from cellulose, may be used to bond other lignocellulose material when subjected to the temperatures and pressures for the periods of time presented hereinafter.

, It is realized that modern chemistry does not have an exact comprehension of the term lignin and that the various commercial lignins are not chemically identical and, in fact, commercial lignin may be an alkali or alkaline earth salt of the organic lignin structure. Moreover, even the lignins obtained from the various lignocellulosic plants or trees vary slightly as to their methoxy content and other properties. The method of obtaining lignin, whether by chemical or mechanical treatment, will afiect the chemical and physical properties of the lignin. Furthermore, the methoxy content of lignin may vary in the lignin obtained from different parts of the same tree or agricultural plant. Nevertheless, all these various lignins as prepared by any of the many known methods are operable and are intended to be embraced within the scope of this invention and its claims.

Examples of a few operable commercial lignins are: Indulin C, a sodium salt of lignin obtained from the sulfate process; and Indulin A, substantially a free or pure lignin also obtained from the sulfate process, and both these Indulins are produced by the West Virginia Pulp and Paper Company; Meadol, a lignin obtained from the soda process and produced by the Mead Corporation; Benaloid, obtained by treating wood with high pressure steam, a product produced by the Masonite Corporation; acid hydrolysis lignin from either the Scholler Process or from the Katzen-Othmer process (Industrial and Engineering Chemistry, vol. 34, page 314) or from any other acid wood hydrolysis process such as that of the Stora Kopparbergs Bergslag Aktiebolag of Falun, Sweden; Goulac, a lignin obtained from the sulfite process and produced by the Robeson Process Company; Silvacon, a lignin produced by the Weyerhaeuser Timber Company from the bark of Douglas Fir; Arborite, a lignin obtained from the soda process and produced by the How- 7 ard Smith Paper Mills; and many others.

Most of the commercially available lignins are contaminated with cellulose or other polysaccharides, the amount present varying from about 20 to about 40 percent; or they are lignin salts of sodium, calcium, or other metals. Others, e. g. Indulin A, on the other hand, are substantially a percent pure or free lignin compounds; and it and similar materials are obtained by acidulating with strong acids the lignin salts that are recovered from pulp and similar manufacturing processes.

We prefer to add lignin to the lignocellulose as an air-dry powder, although the moisture content of the lignin may vary widely as in the case of the lignocellulose itself and still be usable in our invention. This lignin may come directly from a prior, wet manufacturing operation, without drying, if desired. The mesh size of the lignin powder may be important due to desirability of thorough mixing. A fine lignin powder is usually preferred.

To enhance the dispersion of the elemental sulfur throughout the lignocellulose, the sulfur may first be placed in solution with a suitable solvent and then sprayed onto the lignocellulose fibers.

It is also possible to add certain other materials to the mixture of lignocellulose, lignin and sulfur in order to increase the water resistance of the finished board. In particular in preparing wallboard and molded products according to our invention, sulfur is mixed with the lignocellulose with or without added lignin being present, in an amount varying from about one percent to six percent, depending on the species and mesh size of the lignocellulose. The amount of powdered lignin varies from about two percent to about 50 percent, depending on the source and purity of the lignin used and the species of the lignocellulose fibers. .In referring to percentages in all examples, the total amount of naturally moist or air-dry lignocellulose material, the added lignin and sulfur is taken as 100% unless otherwise specified. For example; if in a 10 pound mixture of lignocellulose material, added lignin and sulfur, there is present 20 percent lignin, e. g. Indulin A, and two percent sulfur, this means that there is present in the mixture two pounds of lignin, 0.2 pounds of sulfur, and 7.8 pounds of lignocellulose material.

The mixture is poured in a pan or on a screen or sheet and pressed between the heated platens of a press for a suitable time.

Several very interesting observations were noted after thousands of experiments were completed, and most of the independent variables were carefully studied over a wide range. Firstly, it was found that once the optimum amount of lignin was added to the particular lignocellulose fiber being used, the optimum amount of sulfur to be added to this mixture depended on the mesh size of the lignocellulose fibers being used. The addition of mineral, vegetable, or animal oils or fats, or petrolatum and other hydrocarbons, gives a product which is more water resistant. It is also possible to add fireproofing agents and insecticides to the lignocellulose fibers to make a superior product from these two standpoints. Secondly, the addition of sulfur to a mixture of softwood and lignin produced a very strong, hard board, whereas if a mixture of hardwood species having the same extractives content as the softwood specie, and lignin was used, a

weaker but just as hard a board would be produced.

Thirdly, the lower the extractives content of the particular lignocellulose fibers being used, the less effect the sulfur has in activating the lignin present and added, bonding the lignocellulose fibers and producing a strong, commercial board. (See Table II.)

For example: if three separate mixtures were made, the first mixture comprising Jack Pine (extractives content 4.9%), 30 mesh lignocellulose fibers, 2 percent sulfur and the optimum amount of added lignin (8 percent pure lignin); the second mixture comprising White Pine (extractives content 12.5%), 30 mesh, lignocellulose fibers, 2 percent sulfur, and the optimum amount of added lignin (6 percent pure lignin); and the third and last mixture comprising redwood (extractives content 22%), 30 mesh, lignocellulose fibers, 2 percent sulfur and the optimum amount of added lignin; and each one of these mixtures was heated and pressed at the optimum condition of time, temperature and pressure, the resulting Jack Pine board would have a flexural strength of approximately 4000 pounds per square inch, the White Pine board will have a fiexural strength of approximately 5500 pounds per square inch, and, finally, the redwood board would have a flexural strength of approximately 6500 pounds per square inch.

The mixing of the lignocellulose sulfur and lignin is effected by any conventional mechanical dry mixer to yield a thoroughly blended product. The blended dry mixture is then poured, or dumped, for example, into a pan having a faceplate in the bottom and sidewalls, the whole constituting a deep frame. The mixture is then covered with a wire mesh screen having about 20 wires to the inch and of a size to fit loosely in the pan. The use of this deckel arrangement for making the board may not be necessary, as boards can be made on a continuous basis or simply hot-pressed in between two plates or screen. The purpose of the screen or screens is to facilitate the escape of vapors formed during the hot pressing cycle, The pan is then placed between a pair of heated platens of a hydraulic or equivalent press and subjected to varying pressures for a specified period of time.

6. lower platens during the pressing operation in order to bond the lignocellulose, the sulfur and the added lignin to give a strong wallboard, may

vary anywhere from 180 C. to 300 C., a range between 205 C. and 275 C. being preferred. The pressure applied may vary within wide limits, since pressures within the range from 100 pounds per square inch to 1000 pounds per square inch are operable, though pressures within the range of 300 to 750 pounds per square inch (p. s. i.) are preferred. The time needed for hot-pressing the board may vary from 5 to minutes, although 9 to 15 minutes is usually preferred. While we have found some variation between pressures, temperatures, and time to be possible; i. e., greater time may reduce the pressure used, or vice versa, we have found it most effective to have a minimum temperature of about 205 C. to obtain our desired effect.

The following relationship between platen temperature and board temperature was found by use of thermocouples inserted in the mid-point of the loose and air-dry lignocellulose-ligninsulfur mixture, prior to subjecting this mixture to high temperatures and pressure, to form a board f inches in thickness. The thermocouple wires in these experiments were then molded into the finished board.

Below are presented the results of some experiments and are given to illustrate the nature of the method which we have developed for making a dense, hard, strong material of the nature of wallboard. These results are shown in Table I, from which it is evident that there is an actual chemical change taking place in the making of boards of lignocellulose and sulfur,

with or without the addition of lignin, according to our process, and while the chemical nature of this change is not known, the sulfur appears to activate the lignin of the lignocellulose to make it again act as the bonding agent, just as it did in the original wood or plant material.

Table I Percent Percent Water Percent t r e ll Flexural sorption in y Composition Conditions for pressing tests (p S i) 24 hours sulfur exa 1% soditracted um hyfull immerdroxide sion lution l. 30 mesh white pine wood flour Unpressed Over 100.. None 2. 30 mesh white pine wood flour, 4% sulfur do Over 100.. 3.95 3.1 30 Eesh white pine wood flour, plus 4% sulfur, plus 6% .do Over 100.. 3. 5. 9

ign

Processing time=1l min 4. 30 mesh white pine wood flour, 4% sulfur Pressing temp.= C 500- 600 96. 5 3. 98

Press.=580 p. s. i Pressing tiine=l1 min. 5. 30 mesh white pine Wood flour, 4% sulfur Pressing temp.= C 1, 100-1, 300 63.4 2 1O Press.=580 p. s. i.. Pressing time=ll min. 6. 30 mesh white pine wood flour, 4% sulfur {Pressing temp.=220 C 1, 900-2, 100 29. 6 1 65 Press.=580 p. s. i Pressing time=ll min 7. 30 mesh white pine wood flour, 4% sulfur Pressing temp.=245 C 3, 200-3, 400 20 1 0. 97

I I Press.=580 p. s. 1.... Pressing time=li m 8. 30 mesh white pine wood flour, 4% sulfur, 6% 1igning. grcssing5ggmp=1245 C 6, 000-6, 200 9.6 0 0.3

ress.= p. s.

Other methods of molding used in the art are also applicable, and in some cases it is preferred to use the screen for the bottom of the pan and the faceplate or another screen for the top.

The temperature we employ in the upper and 75 The use of high temperatures effects some type of chemical reaction between sulfur and the components of the wood in the range of about 205 C. to 250 0. Furthermore, the wallboard containing for example 4% sulfur in addition to 6% 7 lignin and pressed for 11 minutes at 245 C. and 580 p. s. i. produced better overall Physical properties than products made employing a lower pressing temperature.

The method of analysis for sulfur was that commonly used for elemental sulfur and comprised dissolving out the free sulfur from a weighted sample of finely divided material by use of a known solvent for sulfur, e. g. carbon bisulfide (CS2). 1

The uncombined or chemically unaltered lignin from each experiment shown in Table I was obtained by extracting the mixture Or final board, with a one percent sodium hydroxide solution since free or pure lignin and lignin salts are completely soluble in a one percent sodium hydroxide solution. The extract was then analyzed by the accepted standard analysis for lignin using concentrated sulfuric acid.

(.5) Swelling due to water absorption Table II Immersion Lignocellulose 2 hours Mois- Thickwater ture ness Mod- Sur- Kind of of Per- Mold- Final Pressof Speulus face B ard lignin and llgnocent ing presing molded eific of hard- Increase No. percent of cellusultcmp., sure time wallgrav' rupness crease in total charge lose in: C. (p. s. 1.) (min.) board ity ture Barcol in thick Specie Mesh size (we in (1 le g t ness cent) inches in in percent cent 16 and higher... Indulin-A 15. 8-9 1 220 600 10 0.175 1.14 4, 500 70 23.0 10. 3 do Indulin-A 2- 8-9 6 270 1, 000 8 0. 160 l. 4, 900 88 24. 2 9. 3 do. Indulin-A 8- 8-9 2 250 800 12 0. 205 1. 20 6, 450 90 16. 0 5. 6 do Indulin-A 15 8-9 1 260 300 0.69 0.88 3, 900 40 25.1 6.3 do Indulin-A 6 8-9 2 250 750 11 0.140 1.15 6,000 65 15.8 3. 5 .d0 Indulin-A 20. 8-9 1 205 100 30 0. 210 1.06 3, 500 58 35. l 14. 2 do Indulin-A 10. 8-9 2 300 350 30 0.833 1.10 3, 920 2 9. 6 11. 9 d0... Indulin-A 15 8-9 1 250 100 60 0. 325 l. 18 4, 320 67 30. 1 10.3 Indulin-A 7... 8-9 3 300 500 5 0.177 1.05 ,070 30.1 8.1 8-9 4 205 600 15 0.218 1. 14 4, 250 53 45. 5 23. 5 8-12 2 250 560 11 0. 188 1.67 4, 200 25. 7 4. 5 8-12 2 250 560 14 0. 230 1. 21 4, 400 21. 5 4. 1 13"-.. E 11 c 2.1 y p t u s 8-12 2 250 560 14 0. 220 1. 28 4, 01 0 81 12.3 3. 2

(fibrous).

8-12 5 250 560 15 0. 246 1. 26 3, 310 67 30. 1 8. 9 8-12 3 250 560 12 0. 185 1. m 3. 800 73 29. 5 10. 3 d0 8-12 2 250 560 13 0. 163 1. 23 4,000 81 12.5 3.0 Induliu-A 9- 8-12 4 250 560 13 0. 180 l. 17 3, 000 78 30. 0 l2. 8 Indulin-A 15 8-12 5 250 560 11 0.165 1.25 4, 500 88 15.0 6. 6 do 8-12 3 250 560 14 0.161 1.18 3, 700 30.1 8. 5 d0 8-12 1 250 560 14 0. 185 1. 16 3, 900 74 27. 3 9. 1 Indulin-A 10- 8-12 1 250 560 12 0. 181 1. 14 4, 000 78 27. 1 7.0 Scholler 14- 8-9 2 250 560 12 0.202 1. 19 4, 850 88 29. 2 11.3 Katzen 20 8-9 2 250 560 14 0.213 1. 14 5,000 90 23. 3 4. 5 Katzen 50. 8-9 2 250 560 16 0. 221 1. 18 5, 600 93 14. 1 6. 1 Goulac 12 8-9 2 250 560 12 0. 195 1. 15 4, 500 62 22. 3 8. 5 Nat. Son. 8... 8-9 2 250 560 12 0.183 1. 18 5, 660 71 14. 2 4.1 Meadol10 8-9 2 250 560 12 0. 185 1. 13 4, 700 67 26. 8 13. 5 Indulin-O 10- 8-9 2 250 560 12 0.186 1.14 4, 900 69 23.4 12.1 Arborite 9 8-9 2 250 560 12 0.181 1.18 6,000 88 11. 5 3. 5 Benaloid 16.- 8-9 2 250 560 12 0. 190 1. 16 5, 850 12.1 3. 8 Silvacon 12 8-9 2 250 560 12 0. 185 1. 19 5, 990 10. 1 2.0 Stora 20 8-9 2 250 560 14 0. 185 1. 20 5, 460 89 18. 5 4. 9 (Kopparbergs hydrolyzed wood) 30 Indulin-A 37. 0 2 250 750 11 0.165 1.19 6, 320 91 10.2 2. 5 30.. Indulin-A 7 5 2 250 750 11 0. 170 1. 16 6, 000 85 12. 5 2. 8 30.. d 15 2 250 750 11 0.171 1.19 6, 84 13. 6 2. 9 30 2 250 750 11 0.168 1. 25 6, 750 85 9. 8 2. 8 30 2 256 750 11 0. 1. 23 6, 620 90 8. 1 2. 7 0 2 250 560 12 0.168 1. 20 6, 000 88 8. 0 2. 9 30 2 250 560 12 0. 165 1. 22 6, 640 91 9. 5 3. 0 50 2 250 560 12 0.166 1. 24 6, 720 92 8. 3 1. 9 8-9 2 250 750 12 0.196 1 13 4, 550 63 15. 7 8. 5 .005" thick. D 6 fi b r a t e (1 8-9 2 250 750 10 0.161 0.99 6, 400 88 8. 3 1. 9

fibers, .5-1.0 long, .001 thick. 49 Yellow pine Indulin-A 3 8-9 2 250 750 12 0 14.5 1 10 6, 650 14. 7 2 9 A s l u n d fibers 50 Masonite pressed 6. 1. 03 5. 500 20.0 8 5 w o o d p u r chased from local lumberman.

In Table II we have listed only those boards made from substantially dry lignocellulose par ticles or fibers and those which, while containing up to 50 moisture, still feel dry. We prefer a dry forming and pressing technique because of the relative clieapness and simplicity of the equipment required for such a dry process; and because of the economy in pressing and the shorter pressing cycle which is possible since t e large amount of water of the wet process does not have to be handled and removed. However, we have also found that using a Wet slurry of the lignocellulose material for making wallboard and such results in a board having a flexural strength in the range as shown in Table II for boards made by the dry process. For example: if 6 percent lignin, e. g. Indulin A, and 2 percent sulfur is added to a slurry of white pine of 30 mesh fibrous material prior to being formed into a mat, and this mixture of added lignin, sulfur and lignocellulose material is later compressed into a cured board at a temperature of 250 C. and a pressure of 600 pounds per square inch for a time of 12 minutes, theflexural strength of the cured board will be approximately 6500 pounds per square inch or higher, and the water resistant properties will also be about the same as those obtained for a dry process board prepared under similar conditions of formulation and pressing.

In our discussion above we have shown the advantages which we have found in the-use of combinations of our preferred materials with lignocellulose in the production of wallboard made directly from sawdust or from other lignocellulosic granules or fibers in either a dry or a wet process. We have also found that we can use the same combinations of materials and under the above specified conditions of pressure, time, and temperature which are required for the making of wallboard in th production of other shapes and articles wherein similar physical properties are desired as in wallboard. It is especially desirable to make such molded objects when the cost of the raw material is important, because the materials we use are very inexpensive. Particularly useful are our methods and the products resulting therefrom in those instances where the cross-sectional dimension of the final object is not too great, and wherein it is possible to mold the material with some provision for the escape of gases, and wherein the shape of the final object is not too complicated and does not require too great an ability of the raw material to flow in filling the mold. In this, case, our preferred combination of materials acts substantially as a molding powder of particular properties and is of comparative cheapness compared to other similar molding powders which have been suggested and are used in the prior art.

We have also found that our combination of materials may be added directly as an upper or lower layer or both in a final application on the surface of an assembly of veneers for the making of plywood. Thus, a smooth, fine surface, similar to that which is produced in making wallboard by our preferred process, is obtained on the surface of the plywood, regardless of any irregularities or imperfections in the plywood itself. Besides eliminating the objectionable grain in some of the rotary cut veneers, irregularities such as knots, etc. may be removed from the surface finish by the application of a mixture of lignocellulosic granules or fibers together with the other materials as specified above. In some cases we have found that the same application of a fine lignocellulosic material, together with added materials as specified above, may be applied to rough lumber or even planed lumber which has imperfections therein; thus, a fine surface is achieved immediately without imperfections, and without surfacing operations which remove and make the wood thinner. The imperfections in the lumber or in the plywood are then removed from vision and are located beneath a hard dense surface having a fine and smooth pattern depending upon the particular type and size of the wood fibers or granules used. In this use we prefer a fine granular or fibrous material having from 30 to or even finer mesh in order to give a thin coating of smooth surface qualities.

We have also found it desirable in certain cases to mix the sulphur and the wood and some other added agents, such as sodium hydroxide or other alkalies such as sodium carbonate, ammonium hydroxide, etc., to give a higher pH of the reacting mass along with the addition of small amounts of water. The amount of alkali, e. g. sodium hydroxide, used may vary preferably from zero to one percent of the total weight of the mix. The amount of water which may be used may vary from 10 to 15% by weight of the total mix, and the preferred proportion of sulphur ranges from 3 to 6% of the total weight of the wood fiber.

Results of experiments made to show the advantage of adding an alkali such as sodium hydroxide to a mixture of lignocellulose and 3 to 6% sulfur, and with other conditions identical, follow:

While this invention is illustrated by many embodiments, it is not to be limited to these embodiments since it is an invention of broad scope.

This invention is a continuation in part of our application Serial Number 75 ,908.

Having thus described our invention, what we claim and desire to secure by Letters Patent, is as follows:

1. The process of making water-resistant molded products consisting essentially of mixing intimately substantially dry lignocellulose with from about 3 to 6 per cent sulfur, and subjecting this mixture to a pressure of from pounds to 1,000 pounds per square inch at a temperature of from C. to 300 C. for a period of 5 to 60 minutes.

2. The process of claim 1 wherein the period varies from 9 to 15 minutes.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 665,229 Kelly Jan, 1, 1901 1,832,307 Ellis Nov. 17, 1931 2,325,570 Katzen et al. July 27, 1943 2,597 Smith et al. May 15, 1951 FOREIGN PATENTS 'Number Country Date 354,001 Great Britain Aug. 1931 

1. THE PROCESS OF MAKING WATER-RESISTANT MOLDED PRODUCTS CONSISTING ESSENTIALLY OF MIXING INTIMATELY SUBSTANTIALLY DRY LIGNOCELLULOSE WITH FROM ABOUT 3 TO 6 PER CENT SULFUR, AND SUBJECTING THIS MIXTURE TO A PRESSURE OF FROM 100 POUNDS TO 1,000 POUNDS PER SQUAE INCH AT A TEMPERATURE OF FROM 180* C. FOR A PERIOD TO 5 TO 60 MINUTES. 